1. Field of the Invention
This invention is directed to an apparatus, in general, which is used for fine-line lithography. In particular, the invention is directed to an improved apparatus which provides thermal and spacing control for a thin mask.
2. Prior Art
In the era of circuit microminiaturization, fine-line lithography is a fundamental fabrication requirement. High resolution lithography is useful in many technical areas such as in the fabrication of magnetic bubble domain devices, semiconductor device, MOS/LSI devices and the like. Many other technological areas are rapidly adopting the techniques of fine-line lithography.
Lithography employing exposure sources other than near U.V. lamps is a known and developing art. In using this type of lithography, various energy sources such as X-ray sources, electron sources and the like are utilized. In the past, these sources have been used with contact or projection techniques. It has been determined that proximity-type masking is more highly desirable than contact masking inasmuch as the mask life tends to be substantially prolonged using the proximity technique. However, it is also been found that use of proximity masks has required a relatively thick mask in order to withstand the problems encountered therewith. Of course, with the thicker mask, less resolution can be obtained with a fine-line lithography technique. Use of thin masks has, typically, been unsuccessful because thin masks tend to absorb energy and thus, heat. Also, thin masks become charged by the energy source. These problems (i.e. thermal and charge absorption) cause the mask to become distorted and, thus, unusable. Consequently, proximity mask techniques are not used significantly even though the advantages thereof are manifold.